1. Technical Field
This disclosure is generally related to surgery, and more particularly to percutaneously deployed medical devices suitable for determining locations of cardiac features or ablating regions of cardiac tissue, or both.
2. Description of the Related Art
Cardiac surgery was initially undertaken using highly invasive open procedures. A sternotomy, which is a type of incision in the center of the chest that separates the sternum, was typically employed to allow access to the heart. In the past several decades, more and more cardiac operations are performed using percutaneous techniques, where access to inner organs or other tissue is gained via a catheter.
Percutaneous surgeries benefit patients by reducing surgery risk, complications and recovery time. However, the use of percutaneous technologies also raises some particular challenges. Medical devices used in percutaneous surgery need to be deployed via catheter systems, which significantly increase the complexity of the device structure. As well, doctors do not have direct visual contact with the medical devices once they are positioned within the body. Positioning these devices correctly and operating the devices successfully can often be very challenging.
One example of where percutaneous medical techniques have been employed is in the treatment of a heart disorder called atrial fibrillation. Atrial fibrillation is a disorder in which spurious electrical signals cause an irregular heartbeat. Atrial fibrillation has been treated with open heart methods using a technique known as the “Cox-maze procedure.” During this procedure, physicians create lesions in a specific pattern in the left and right atria that block various paths taken by the spurious electrical signals. Such lesions were originally created using incisions, but are now typically created by ablating the tissue with radio-frequency (RF) energy, microwave energy, laser energy or cryogenic techniques. The procedure is performed with a high success rate under the direct vision that is provided in open procedures, but is relatively complex to perform percutaneously because of the difficulty in creating the lesions in the correct locations. Various problems, potentially leading to severe adverse results, may occur if the lesions are placed incorrectly.
Key factors which are needed to dramatically improve the percutaneous treatment of atrial fibrillation are enhanced methods for deployment, positioning, and operation of a treatment device. It is particularly important to know the position of the elements which will be creating the lesions relative to cardiac features such as the pulmonary veins and mitral valve. The continuity and transmurality characteristics of the lesion patterns that are formed can impact the ability to block paths taken within the heart by spurious electrical signals.
Several methods have been previously developed for positioning percutaneously deployed medical devices within the heart. For example, commonly assigned U.S. Patent Application Publication No. 2008/0004534 A1, which is herein incorporated by reference in its entirety, describes various intra-cardiac mapping systems based on detecting the ports through which blood flows in or out of a heart chamber. Commonly assigned U.S. Patent Application Publication No. 2009/0131930 A1, which is herein incorporated by reference in its entirety, describes a device that is percutaneously guided to a cavity of a bodily organ (e.g., a heart). The device can discriminate between fluid within the cavity (e.g., blood) and tissue that forms an inner or interior surface of the cavity (e.g., surface tissue) to provide information or mapping indicative of a position, orientation, or both position and orientation of the device in the cavity. Discrimination may be based on flow or some other characteristic, for example electrical permittivity or force. The device can selectively ablate portions of the surface tissue based at least on the information or the mapping. In some cases, the device may detect characteristics (e.g., electrical potentials) indicative of whether ablation was successful. The device includes a plurality of transducer elements that are intravascularly or percutaneously guided in an unexpanded configuration and positioned proximate the surface tissue in an expanded configuration. Various expansion mechanisms that include helical member(s) or inflatable member(s) are described. Other forms of expansion mechanisms are described in commonly assigned U.S. Provisional Patent Application No. 61/435,213; U.S. Provisional Patent Application No. 61/485,987; U.S. Provisional Patent Application No. 61/488,639; and U.S. Provisional Patent Application No. 61/515,141 which are each herein incorporated by reference in their entirety.
Atrial fibrillation is but one example of a cardiac surgery that requires effective mapping systems that are percutaneously deliverable to various intra-cardiac cavities. The mapping systems should allow for the improved determination of the relative position of anatomical features within the intra-cardiac cavity such as pulmonary veins and mitral valve with respect to a portion of the system that is percutaneously delivered.